Backrest device for a vehicle seat

ABSTRACT

Backrests for vehicle seats are disclosed including a support attached to a frame including a plurality of resilient springs and a corresponding plurality of stroke limiters for permitting the resilient springs to move through a predetermined stroke and absorb a load within a first load range and limiting further stroke of the resilient springs within a second load range, one of the resilient springs and the stroke limiters including a fastener for attachment to the frame and one of the resilient springs and stroke limiters including a second fastener for attachment to the support.

FIELD OF THE INVENTION

The present invention relates to apparatus for a vehicle seat backrest.

BACKGROUND OF THE INVENTION

Conventional backrests for vehicle seats are provided with resilientcompliant means having only a comfort function, i.e. they are functionalto provide an even and comfortable support for the passenger's back andwill adapt to normal back motions during a normal state of use. In caseof a rear-end collision, the back will be subjected to excessiverearwards movement in the backrest, and, furthermore, accumulation ofresilient energy will cause the back to recoil forward, creating a riskof so called whiplash injuries.

From International Application No. WO 95/11818 a backrest is known,which has been designed with the aim of reducing whiplash injuriescaused by rear-end collisions. According to the prior art, this has beenachieved by arranging separate stroke-limiting means, such as bands orlinks having attachment points separate from the fastening points of thesprings. The means of attachment and the design of the spring means andthe stroke-limiting means are very critical with regard to the totalfunction of compliance of the backrest, for normal loads as well asextreme loads, such as during a collision.

An object of the present invention is to provide apparatus for abackrest in which the compliant members can have accurately specifiedproperties.

SUMMARY OF THE INVENTION

In accordance with the present invention, this and other objects havenow been realized by designing the compliant member of such backrestswith each spring member and stroke limiting member being integralcomponents which can be produced with specified properties with respectto their compliance characteristics.

In accordance with the present invention, applicants have invented abackrest for a vehicle seat comprising a frame defining a central zone,a support member, a plurality of compliant members for supporting thesupport member within the central zone, whereby the compliant membersand the support member can absorb the load from a person seated in thevehicle seat, the plurality of compliant members comprising a resilientspring member and a corresponding stroke-limiting member for permittingthe resilient spring member to move through a predetermined stroke andabsorb a load within a first load range and limiting further stroke ofthe resilient spring member within a second load range, one of theresilient spring member and the stroke-limiting member including a firstfastener for attachment to the frame and one of the resilient springmember and the stroke-limiting member including a second fastener forattachment to the support member. In a preferred embodiment, at leastone of the plurality of compliant members comprises a plasticallycompliant member whereby the one of the plurality of compliant membersexhibits plastic compliance at a load exceeding the second load range.Preferably, the plastically compliant member is disposed in series withone of the resilient spring members. In another embodiment, however, theplastically compliant member is disposed in parallel with one of theresilient spring members. Preferably, one of the stroke-limiting membersis disposed in series with the plastically compliant member.

In accordance with one embodiment of the backrest of the presentinvention, the backrest includes stroke-limiting means for limitingfurther stroke of the resilient spring member within a third load rangeabove the load exceeding the second load range.

In accordance with another embodiment of the backrest of the presentinvention, the resilient spring member comprises a coil-type compressionspring and wherein the stroke-limiting member comprises first and secondfastening members, the first fastening member including a first endincluding the first fastener and the second fastening member including afirst end including the second fastener. In a preferred embodiment, thefirst and second fastening members extend through the coil-typecompression spring, the first fastening member including a second endattached to one end of the coil-type compression spring and the secondfastening member including a second end attached to the other end of thecoil-type compression spring, whereby motion of the first and secondfastening members causes compression of the coil-type compression springsuch that stroke-limiting occurs upon complete compression of thecoil-type compression spring.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, detailed description, the present invention will bedescribed in detail with reference to the accompanying drawings, inwhich:

FIG. 1 is a front, elevational, schematic, partially cutaway view of avehicle seat provided with a backrest according to the presentinvention;

FIG. 2 is a front, elevational view of a compliant member provided withstroke-limiting members in accordance with the present invention;

FIG. 3 is a front, elevational, exploded view of a compliant memberprovided with stroke-limiting members in accordance with the presentinvention;

FIG. 4 is front, elevational view of a compliant member provided with astroke-limiting member in accordance with the present invention;

FIG. 5 is a front, elevational view of compliant member provided with astroke-limiting member in accordance with another embodiment of thepresent invention;,

FIG. 6 is a diagrammatic representation of the characteristics ofcompliant member in accordance with FIGS. 2-5;

FIG. 7 is a front, elevational view of a compliant member provided withthe stroke-limiting member and a plastically compliant member inaccordance with another embodiment of the present invention;

FIG. 8 is a front, elevational view of a complaint member provided witha stroke-limiting member and with a plastically compliant member inaccordance with another embodiment of the present invention;

FIG. 9 is a diagrammatic representation of the characteristics of thecompliant members shown in FIGS. 7 and 8;

FIG. 10 is a front elevational view of a plastically compliant member inaccordance with one embodiment of the present invention;

FIG. 11 is a front, elevational view of the plastically compliant membershown in FIG. 10 under an extreme load;

FIG. 12 is a front, elevational view of plastically compliant member inaccordance with another embodiment of the present invention;

FIG. 13 is a front, elevational view of the plastically compliant memberof FIG. 12 under an extreme load;

FIG. 14 is a front, elevational view of a plastically compliant memberin accordance with another embodiment of the present invention;

FIG. 15 is a front, elevational view of the plastically compliant memberof FIG. 14 under an extreme load;

FIG. 16 is a front, elevational view of the plastically compliant memberin accordance with another embodiment of the present invention; and

FIG. 17 is a front, elevational view of the plastically compliant memberof FIG. 16 under an extreme load.

DETAILED DESCRIPTION

Referring to the Figures, in which like reference numerals refer to likeelements thereof, FIG. 1 shows, schematically, the construction of abackrest 1 in a vehicle seat 2 for a motor vehicle. The figure showsthat the backrest 1 is generally constructed as a frame 3 having twoside members, 4 and 5, and a top member 6. The backrest extendsconventionally upward from the rear edge of a seat member 7 of thevehicle seat and is attached thereto by a lockable joint for adjustmentof the inclination of the backrest 1. The frame encloses an area 8, inwhich a support member 9 is suspended. The support member is arranged tobe flexibly suspended in the frame by means of a multitude ofresiliently compliant members 10, attached between the support memberand the frame. These members comprise the load-carrying elements of thebackrest, which are embedded in a cushion of well-adjusted softness andenclosing upholstery. In FIG. 1, the compliant members 10 are, for thesake of simplicity, shown as simple tension springs, which are, however,according to the present invention, integrated with other elements, aswill be described in greater detail below.

The support member 9 preferably consists of a flexible webbing, socalled net webbing or pullmaflex webbing, i.e. a flexible, compliantunit functioning to absorb the load emanating from the back of a personsitting in the vehicle seat. This is performed in cooperation with thecompliant members, in the illustrated example being attached between thetwo side members, 4 and 5, of the frame, and the support member 9. Thelatter is, in the illustrated example, of rectangular shape having twoside edges, 11 and 12, spaced from the frame side members, 4 and 5,respectively. The compliant members extend, in the illustrated example,from the respective side member, 4 and 5, of the frame 3 to theneighbouring side edge, 11 and 12, of the support member 9. The supportmember in the illustrated example consists of two rigid wires or rods,13 and 14, forming its side edges, 11 and 12, with a multitude offlexible threads 15 stretched between the rods.

The compliant members 10 are provided at each end with fasteningelements, attached to fastening points in the frame 3 and the supportmember 9, respectively. The fastening elements consist of, for example,hook-shaped elements, hooked into holes in the frame, and around therods, 13 and 14, respectively. Through the compliance of the compliantmembers, a difference s in the distance between the fastening elementsis allowed when absorbing, mainly in the longitudinal direction of thecompliant members, the load and the movement which is generally directedtowards the support member, i. e. being directed transversely theretoand thus to the longitudinal direction of the members. Above thebackrest there is a head restraint 17, which may be of conventionaldesign but is of major importance regarding the supporting functionduring extreme load, such as during a rear-end collision caused byanother vehicle.

FIG. 2 illustrates a first example of a compliant member, in thisexample designated 18 and comprising on one hand a spring member 19 andon the other hand a stroke-limiting member 20, integrated with thespring member. The compliant member exhibits a hook-shaped fasteningelement, 21 and 22, at each end, for attachment either to the frame 3 orto the support member 9, or vice versa. The spring member 19 iscomprised of a tension type coil spring, for example made of coil woundspring steel wire, continuing at its ends into the fastening elements,21 and 22. The stroke-limiting member 20 is at one end 23 fastened toone end 24 of the spring member, and extends along the latter with astraight portion 25, being principally of fixed length and having a stop26 in the form of a hook-like portion, located at a predetermineddistance s₁ from the other end 27 of the spring member in its unloadedcondition. The stroke limitation is achieved by the end 27 of the springmember being pulled out the distance s₁ in the excessively loadedcondition of the compliant member, whereby the hook-like portion 26hooks into the winding of the spring member at its end 27.

FIGS. 3 and 4 illustrate another example of a compliant member, in thiscase designated 28. For the sake of clarity, the compliant member isshown in an exploded view in FIG. 3, whereas FIG. 4 shows the assembledmember. The spring member 29 is in this case a compression spring in theform of a coil spring, which in the illustrated unloaded condition isexpanded. The stroke-limiting member 30 is created indirectly in thisexample, by two identical parts, 31 and 32, in the shape of V-bent wiresections, meeting at their tip ends 33, creating fastening elements forthe compliant member and being attached to the remote end of said springmember 29. At their opposite ends, two hook-like sections, 34 and 35,are provided. As is shown in FIG. 4, in the assembled compliant member24, the two elements, 31 and 32, are passed through the spring member29, one from each side, with the tip end 33 leading, until the hook-likesections, 34 and 35, in practice hook onto the respective ends, 36 and37, of the spring member 29. The two tip ends, 33 and 38, thus eachcreate one fastening element of the assembled component, to be attachedto the frame 3 or the support member 9, respectively. Consequently, inthis case the two elements, 31 and 32, as such are not stroke-limitingmembers, but are creating a stroke limitation by causing an invertedmovement of the spring member, i.e. a pulling load between the fasteningelements, 33 and 38, creates a pushing load on the spring member 29,because the hook-like sections, 34 and 35, by hooking onto the ends, 36and 37, of the spring member compresses the latter until it “bottomsout”, i. e. reaches a butt contact end position, which creates thestroke limitation.

A variant compliant member 39 is illustrated in FIG. 5, in which thespring member 40 is a coil type compression spring, shown in itsunloaded condition and exhibiting hook-like fastening elements, 41 and42, extending by means of straight wire sections, 43 and 44, through thespring member and being equipped also at their opposite ends withhook-like-elements, 41′ and 42′, which are each hooked onto that end, 45and 46, respectively, of the spring member which is located opposite thecorresponding fastening elements, 41 and 42. The same function as in theembodiment of FIG. 4 is obtained, i.e. a pulling of the fasteningelements, 41 and 42, entails a compression of the spring element 40until it “bottoms out,” whereby a stroke limitation is achieved.

FIG. 6 schematically shows the characteristics of the above discussedcompliant members, whereby the compliant movement of the compliantmember is designated by s and the load is designated by F. The compliantmovement is, in the illustrated example, proportional to the load, butmay also be progressive, up to a travelled distance s₁, which range ofmovement is used during normal loads from the person's back, i.e. duringnormal conditions of vehicle use within a first load range, up to alimit load F₁. By extreme load, such as during a rear-end collision, thelimit load F₁ is exceeded, and the maximum movement stroke s₁ isreached, causing the stroke-limiting member to be activated, so that thedistance of movement will not increase in spite of increasing load.Through this action, the compliant members are prevented from yieldingfurther, whereby the support member will not allow the person's back tosink further into the backrest, thereby reducing the risk of a whiplashinjury.

FIG. 7 illustrates a compliant member 47 constructed from threeintegrated members influencing the compliance, that is, besides thespring member 40 and the stroke-limiting member, a plastically compliantmember 48, in this example being arranged in series with the other twomembers. In the example shown in FIG. 7, the spring member 40 and thestroke-limiting member is of a design similar to that of FIG. 5, but itmay alternatively be of a different design, for example according to theexamples illustrated in FIGS. 2 and 3. The plastically compliant member48 is integrated into the straight section between the attachment pointat the end of the spring member 46 and the attachment point 42 of thecompliant member, and is in the illustrated example designed, inrelation to the resilient member 40, as a highly shape-resistant,Z-shaped or spiral-shaped loop. Its shape resistance is dimensioned suchthat the distance between its two end points, 49 and 50, remainsgenerally constant, on one hand during normal use, i.e. a first loadrange, and on the other hand during a second load range of elevatedload, during stroke limitation. If the load increases even further, theplastically compliant member will yield plastically until the distancebetween the two points 49 and 50 reaches an end position, at which theplastic deformation ceases and a further stroke limitation will occurfor still higher loads.

FIG. 8 illustrates an alternative example with a spring member 51 in theform of a tension spring and, in parallel thereto, is attached both astroke-limiting member 52 and a plastically compliant member 53connected in series with each other. One end of the spring member andthe corresponding end of the stroke-limiting member exhibit a commonfastening member 54, while the opposite end of the spring member and theexternal end of the plastically compliant member also exhibit a commonfastening member 55.

FIG. 9 shows, schematically by means of a diagram, characteristics ofthe compliant members of the type illustrated by examples in FIGS. 7 and8, i. e. exhibiting a spring member as well as a stroke-limiting memberand a plastically compliant member. During a primary, normal load range,the resilient compliance thus takes place over a distance of movement upto the distance s₁, whereupon the stroke limitation occurs at a loadlimit F₁. In case of further load inside a range up to the load F₂ nocompliance occurs, whereupon the plastically compliant member will beactivated up to a predetermined distance s₂, after which a second strokelimitation will occur in case of further increased load. In the case ofFIG. 9, a resilient compliance will, however, remain also for loadsabove F₂, which is indicated by a dot-dashed line.

FIG. 10 shows an independent view of the plastically compliant member 48of FIG. 7. The plastic deformation and absorption of energy will thusoccur at a certain load, at which the bent or spirally wound wire willbe straightened out so that the distance between the two points, 49 and50, will increase to a maximum value, changing the compliance by adistance s₂.

The example according to FIGS. 12 and 13 shows an alternative embodimentof the plastically compliant member, designated by reference numeral 57.In this example, that member is designed as a wire extending in a tube58, having a forward portion 59 and a return portion 60. This creates anend portion 61 that can function as a fastening element for attachmenteither to the frame of the vehicle seat or to the support member andwhich may for example consist of an eye 62. The plastic compliance willoccur at a certain tension load in the forward portion 59, which isattached to the spring member of the compliant member, forcing thereturn portion 60 to yield through bending and subsequent straightening.

FIGS. 14 and 15 show a further example of a plastically compliant member63, consisting of a wire portion 64, which at one end is attached to thespring member, e.g. a tension spring, and at the other end 65 has alager diameter, which is furthermore larger than a hole 66, throughwhich the wire 64 will stretch and be pulled out at a predeterminedexcessive load. The plastic compliance is created by the thicker portionof the wire being plastically deformed by passing through the hole 66.

FIGS. 16 and 17 illustrate a further example of the plasticallycompliant member 67. In this example, one end 69 of a wire portion 68 isattached to the spring member and the other end 70 is fastened to theremote end of a deformable distance element 71 that is attached to aplate 72 having an opening 73 through which the wire extends. Thedistance element is, for example, designed as a cylinder, which, at thepredetermined overload, will buckle and allow the end 70 to travel inthe direction of said plate 72.

To summarise, various examples of compliant members, for attachmentbetween the frame 3 and the support member 9 in the backrest of avehicle seat have been demonstrated and described. Without exception,the compliant members have been designed as integrated components havingresilient and stroke-limiting members, and in some cases also plasticmembers, arranged to have a common point of attachment for eachcomponent, to the frame and the support member, respectively, and beingarranged either in series or parallel, or in a combination of series andparallel connection. The compliant members are mainly made of a wirematerial and can be dimensioned for providing specific propertiesregarding compliant movement and load limits.

The compliant members 10 have, during normal use, i.e. normal use of thevehicle, only a comfort function, whereby they provide, together withthe support member, in co-operation with stuffing and upholstery of thebackrest, an even support for the back, and compliance for normalmovement of the back. During extreme loads, such as a rear-endcollision, the compliant members 10 provide a load-absorbing functionand a recoil-dampening function, on one hand preventing the back frombeing pressed too far into the backrest 1, and on the other hand notrecoiling forward in a limited movement, which might otherwise entaildetrimental loads on the spinal column and the neck vertebrae, whencombined with the more limited compliance of the head restraint.

The present invention is not limited to the examples shown in thedrawings and described above. The number of compliant members 10 betweenthe frame 3 and the support member 9, and their location may vary fromseat to seat. For example, compliant members may also be attachedbetween the top member and the support member 9. The latter may furtherbe constructed in a different way. At the lower portion of the majorityof backrests, an adjustable sway-back support is provided, which shouldhave a larger compliance than the compliant members during extreme load,in such a manner that the sway-back support will not prevent the abovediscussed compliance of the backrest as a whole.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A backrest for a vehicle seat comprising a framedefining a central zone, a support member, a plurality of compliantmembers for supporting said support member within said central zone,whereby said compliant members and said support member can absorb theload from a person seated in said vehicle seat, said plurality ofcompliant members comprising a resilient spring member and acorresponding stroke-limiting member for permitting said resilientspring member to move through a predetermined stroke and absorb a loadwithin a first load range and limiting further stroke of said resilientspring member within a second load range, one of said resilient springmember and said stroke-limiting member including a first fastener forattachment to said frame and one of said resilient spring member andsaid stroke-limiting member including a second fastener for attachmentto said support member, wherein at least one of said plurality ofcompliant members comprises a plastically compliant member whereby saidone of said plurality of compliant members exhibits plastic complianceat a load exceeding said second load range, wherein said plasticallycompliant member is disposed in series with one of said resilient springmembers.
 2. A backrest for a vehicle seat comprising a frame defining acentral zone, a support member, a plurality of compliant members forsupporting said support member within said central zone, whereby saidcompliant members and said support member can absorb the load from aperson seated in said vehicle seat, said plurality of compliant memberscomprising a resilient spring member and a corresponding stroke-limitingmember for permitting said resilient spring member to move through apredetermined stroke and absorb a load within a first load range andlimiting further stroke of said resilient spring member within a secondload range, one of said resilient spring member and said stroke-limitingmember including a first fastener for attachment to said frame and oneof said resilient spring member and said stroke-limiting memberincluding a second fastener for attachment to said support member,wherein at least one of said plurality of compliant members comprises aplastically compliant member whereby said one of said plurality ofcompliant members exhibits plastic compliance at a load exceeding saidsecond load range, said stroke-limiting member including stroke-limitingmeans for limiting further stroke of said resilient spring member withina third load range above said load exceeding said second load range.